Ochotona pusilla occidentalis, Erbajeva & Montuire & Chaline, 2001

Erbajeva, Margarita A., Montuire, Sophie & Chaline, Jean, 2001, New ochotonids (Lagomorpha) from the Pleistocene of France, Geodiversitas 23 (3), pp. 395-409 : 401-406

publication ID	https://doi.org/ 10.5281/zenodo.5374515
persistent identifier	https://treatment.plazi.org/id/D74E8233-FFC8-490C-CE1E-FEF3D46234F5
treatment provided by	Marcus
scientific name	Ochotona pusilla occidentalis
status	subsp. nov.

Treatment

Ochotona pusilla occidentalis n. ssp. ( Figs 3 View FIG ; 4 View FIG A-H, Q)

HOLOTYPE. — Right mandibular ramus with p3- m3, with incisor, without angular process and condyle, University of Burgundy (F-3414) ( Figs 3 View FIG ; 4A View FIG ).

TYPE LOCALITY. — La Fage, level 4, Corrèze, France.

ETYMOLOGY. — occidentalis: found in France, western Europe.

HYPODIGM. — In addition to the holotype, a large number of specimens are known: 1) La Fage (Corrèze): 1 fragment of dex mandible with p4-m3 (F-3414bis); 1 fragment of sin mandible with p3-m3 without incisor, angular process and condyle (F-3444); 1 fragment without teeth (F-3444a); 5 fragments of mandible in various conditions with teeth and without teeth (F-3444bis); 3 fragments of mandible without teeth (F-3001, F-3001a, F-3001bis); 2 fragments of dex mandible with p4-m2 (F-1244, F-1244a); 1 fragment of sin mandible with p3-m3 (F-4862) and 1 fragment of dex mandible with p4-m3 (F-4862a); 3 fragments of maxilla with various teeth (F-4862bis).

2) Baume de Gigny or Loisia cave (Jura): 1 fragment of dex mandible with p3-m3 with incisor, without angular process and condyle (G-61000); dex mandibles with various teeth (G-61002-61008); dex mandibles without teeth (G-61009-61016); sin mandibles with various teeth (G-61017-61020); sin mandibles without teeth (G-61021-61023); fragments of maxilla dex with various teeth (G-61024-61025); fragments of maxilla sin with various teeth and without teeth (G-61026-61032); isolated teeth: p3 (G- 61001); p4 (G-61033-61047); m1 (G-61048- 61051); m2 (G-61052-61061); m3 (G-61062- 61066); P3 (G-61067-61081); P4 (G-61082- 61101); M1 (G-61102-61123); M2 (G-61124- 61135); upper incisors (G-61136-61162); lower incisor (G-61163); fragments of postcranial skeleton (G- 61164-61169).

HORIZON, LOCALITY AND GEOLOGICAL AGE. —La Fage, level 4, middle and late Pleistocene.

DIAGNOSIS. — The mandibular ramus is rather short, comparatively low and robust. P2 is oval, its inner part is flattened anteriorly and the inner-posterior wall of the tooth is rounded.

DIFFERENTIAL DIAGNOSIS. — A small sized pika of the “ pusilla ” group. It differs from extant Ochotona pusilla Pallas in its short mandibular ramus, the mandible being almost the same height as that of the Recent form ( Figs 3A View FIG ; 6A View FIG ). Moreover, these two ochotonids differ in the slightly smaller size of p 3 in the extant pika, in P2 having a shorter anterior fold and in the more rounded shape of the inner-anterior part in O. p. pusilla ( Fig. 4 View FIG A-H, N, Q, T). The pika from France differs from the second extant subspecies O. p. angustifrons Argyropulo in its smaller size. Average alveolar lengths of P2-M2 and p3-m3 of extinct pika are respectively 7.4 and 7.3 compared with 7.8 and 7.8 for the extant subspecies. They differ also in the distinctively high and narrower mandibular ramus of the latter at p4 ( Table 3). Ochotona pusilla occidentalis n. ssp. differs from O. p. angustifrons in that its P2 has only one anterior fold, the P2 of the latter, apart from a deep anterior fold, having a shallow, cement-free depression on the antero-labial face ( Fig. 4V View FIG ). Ochotona pusilla from France differs from all extinct taxa of the “ pusilla ” group in its size: being somewhat smaller than pikas from Emirkaya ( Turkey) and from Barakaevo Cave ( Russia) (p3 length is equal to or greater than 1.2) and being larger on average than ochotonids from the Aktogai locality ( Kazakhstan), and the Malta, Yar and Razdolinskaya localities (eastern Siberia, Russia) (p3 length ranges from 0.9 to 1.05).

REMARKS

More than 200 remains of at least 24 individuals from Gigny and 25 remains of not fewer than six individuals from La Fage can be attributed to a small Ochotona species. Considering the number of mandibles, the total material belongs to no fewer than 30 individuals. Judging by the main characters and the proportions of skull remains and mandibles, the ochotonids from the La Fage and Baume de Gigny localities belong to Ochotona pusilla . This material allows us to describe their morphology. Closer examination of these extinct small pikas from France and comparison with all known specimens of Ochotona pusilla has shown that the small ochotonids from the La Fage and Gigny localities differ from all taxa of the “ pusilla ” group in size and in mandible and tooth morphology ( Figs 3 View FIG ; 4 View FIG A-H, Q; Tables 2; 3).

MORPHOLOGICAL DESCRIPTION

The studied specimens are housed in the collections of the University of Burgundy, UMR CNRS BIOGEOSCIENCES 5561. The mandibles are small and robust at p4, while the diastema is short ( Table 3). The lower incisor extends posteriorly along the ventral border of the mandible approximately in a line below p4 with well-developed tubercles on both the lingual and labial sides of the mandibular ramus at the root end of the incisor. A rather deep groove beginning under the inner tubercle extends posteriorly along the ventral border of the mandible approximately to the end of the row of teeth on the lingual side of the mandible ( Fig. 3 View FIG B-D). Almost all of the teeth (upper – P2, P3, P4, M1, M2 – and lower – p3, p4, m1, m2, m3) are preserved in the specimens.

The first lower premolar (p3) of Ochotona pusilla occidentalis n. ssp. is triangular, consisting of two conids with a wide confluence. The anteroconid of p3 is comparatively large with a rounded and blunt anterior part in adult individuals and with a rather sharp one in young individuals. Its length and width are almost equal ( Table 3). The posteroconid of p3 is about two thirds narrower anteriorly than posteriorly because its lingual side is greatly extended intero-posteriorly ( Fig. 4 View FIG A-H). p3 has two persistant external folds and one internal fold filled with cement. The depth of the antero-external and antero-internal folds varies greatly. The lower molariform teeth are similar in shape to those of other Ochotona . The largest of the lower teeth is m1 and the smallest is p4. The talonid of the p4 is wider than the trigonid. The talonids of m1 and m2 are almost as wide or slightly narrower than the trigonid. m3 consists of a single narrow column ( Fig. 5B View FIG ).

The upper teeth, except for P2, do not differ morphologically from the corresponding teeth of all Ochotona pusilla taxa. The single-lobed P2 ( Fig. 4Q View FIG ) is oval with a narrow and rather deep, cement-filled anterior fold directed posteroexternally. The anterior side of its inner part is flat and its external part is oval. The trapezoidal P3 is flattened, with its anterior part much narrower than the posterior one. Its deep, cement-filled, antero-labial fold begins at a point at one quarter of the tooth width and finishes at approximately the same level. The hypostria is short and filled with thin cement. P4, M1 and M2 have deep, cement-filled hypostriae. M2 has a posteriorly directed process as in all Ochotona species ( Fig. 5A View FIG ).

COMPARISONS

Ochotona pusilla occidentalis n. ssp. differs from all of the taxa of Eurasian Ochotona pusilla View in CoL , particularly from Ochotona pusilla spelea Owen, 1846 (Kent’s Hole, UK), in that it is either smaller or larger and has different tooth proportions and mandible structures. It differs from extant species and from extinct taxa from the Ukraine (Loc. Novgorod-Severskyi), from Crimea (Loc. Alimovskyi naves and Adji Koba) and from Transcaucasus (Barakaevo Cave, Azyh) in both its small size and its much shorter diastema ( Gromov 1961; Rekovets 1985; Erbajeva 1988). The taxon from France is slightly smaller than the forms from the Urals (Medvezhia Cave, Yarsino and Alabuga localities), from Moldavia (Loc. Brinzeny) ( Kuzmina 1965; Maleeva & Federyagina 1984; Lozan 1970; Smirnov et al. 1986) and from Germany (Obere Franken). However it is as large or slightly larger than the Siberian pika from the Yar locality on the Biryusa River (eastern Siberia), which also has small and low mandibles. Ochotona pusilla occidentalis n. ssp. differs from both extant subspecies in having more robust, shorter and mandibles ( Figs 3 View FIG ; 6 View FIG ) as well as in its tooth morphology. Ochotona pusilla pusilla (Pallas, 1769) View in CoL possesses a small and narrow P2 and a triangular P3 ( Fig. 4T View FIG ). Ochotona pusilla angustifrons Argyropulo (1932) View in CoL is characterized by a wide P2 and the flattened shape of P3 ( Fig. 4V View FIG ). The pika from France has a wider P2 ( Fig. 4Q View FIG ) than the P2 of Ochotona pusilla pusilla View in CoL and one that is much narrower than the corresponding tooth of O. p. angustifrons. Ochotona pusilla occidentalis n. ssp. is characterized by wider confluences between the anteroconid and posteroconid of p3 than in extant species. Ochotona View in CoL from the Gigny and La Fage localities differs from all extinct Eurasian subspecies in its anteroconid shape and by the highly variable depth of the antero-inter-

A B

nal and antero-external folds of this tooth. While the extinct pika from the Orgnac-3 locality ( France) housed in the Muséum d’Histoire naturelle of Lyon resembles Ochotona pusilla occidentalis n. ssp. in p3 morphology and in mandible structure, it differs from the latter in its narrower confluence between antero- and posteroconid and its wider p3 ( Fig. 4I View FIG ).

HISTORY OF STEPPE PIKA

It is known that the history of Ochotona pusilla unfolded in western Siberia at least until the end of the late Pliocene – onset of the Pleistocene

( Erbajeva 1988, 1994). Accordingly its ancestors may have evolved in Asia. The first pika belonging to Ochotona pusilla appeared in Asia at the end of late Pliocene-beginning of the Pleistocene. It was represented by a primitive subspecies Ochotona pusilla aktogaiensis Savinov, 1981 found at the Aktogai locality in Kazakhstan with an associated Allophaiomys fauna ( Kozhamkulova et al. 1981). This fauna suggests a relatively mild climate. The pika similar to this taxon found in western Siberia at the Kizikha locality is of the same geological age. Probably Ochotona sp. from the Emirkaya locality ( Turkey) associated with Hypolagus sp. can be considered as one of the early Ochotona pusilla too ( Montuire et al. 1994). During the middle and late Pleistocene successive glacial and interglacial stages resulted in periodical changes in the palaeoenvironment. With col- der and drier climates, steppe became widespread in Eurasia. At that time, vast areas of Eurasia were covered by the characteristic steppe-tundra ecosystem also known as “mammoth steppe”. Throughout Pleistocene times, Asia was extensively connected with Europe with no major barriers such as ice-sheets. This evidence makes it clear that Asian steppe faunas such as ochotonids, jerboas and lagurids migrated extensively to Europe. At that time Ochotona pusilla radiated widely and diversified considerably. The vast plains of Europe and Asia from southern England and France in the West, from the Negev and Turkey in SW Asia to eastern Siberia in the East were inhabited by Ochotona pusilla ( Fig. 7 View FIG ). New fossil finds of this species in three Prebaikalian localities ( Malta, Yar and Razdolinskaya) allow us to extend its range further East than was known previously when it was thought that the Yenisey River marked the eastern boundary of the distribution area of steppe pika. A number of middle and late Pleistocene subspecies and forms have been recognized within the species Ochotona pusilla ( Erbajeva 1988) . During postglacial time until the Holocene, the more moderate climate was associated with the reestablishment of forest and grassland. This restricted the range of Ochotona pusilla . Holocene fossil remains are known from the Crimea, Hungary and even in historical times there are considerable data on the occurrence of Ochotona pusilla in SE Europe and the southern Urals. Towards recent times Ochotona pusilla seems to have been gradually restricted to its current range in Eurasia. The total recent area includes steppes from the Middle Volga East through North Kazakhstan and the southwestern slopes of the Altai mountains to the border of China ( Fig. 7 View FIG ).